Quantitative assessment of unobserved confounding is mandatory in nonrandomized intervention studies

Measurement Error and Misclassification in Orthopedics: When Study Subjects are Categorized in the Wrong Exposure or Outcome Groups

Datasets available for orthopedic research often contain measurement and misclassification errors due to errors in data collection or missing data. These errors can have different effects on the study results. Measurement error refers to inaccurate measurement of continuous variables (eg, body mass index), whereas misclassification refers to assigning subjects in the wrong exposure and/or outcome groups (eg, obesity categories). Misclassification of any type can result in underestimation or overestimation of the association between exposures and outcomes. In this article, we offer practical guidelines to avoid, identify, and account for measurement and misclassification errors. We also provide an illustrative example on how to perform a validation study to address misclassification based on real-world orthopedic data. Please visit the followinghttps://youtu.be/9-ekW2NnWrsor videos that explain the highlights of the article in practical terms.

Impact of influenza vaccination on amoxicillin prescriptions in older adults: A retrospective cohort study using primary care data

Background

Bacterial infections of the upper and lower respiratory tract are a frequent complication of influenza and contribute to the widespread use of antibiotics. Influenza vaccination may help reduce both appropriate and inappropriate prescribing of antibiotics. Electronic health records provide a rich source of information for assessing secondary effects of influenza vaccination.

Methods

We conducted a retrospective study to estimate effects of influenza vaccine on antibiotic (amoxicillin) prescription in the elderly based on data from the Clinical Practice Research Datalink. The introduction of UK policy to recommend the influenza vaccine to older adults in 2000 led to a substantial increase in uptake, creating a natural experiment. Of 259,753 eligible patients that were unvaccinated in 1999 and aged≥65y by January 2000, 88,519 patients received influenza vaccination in 2000. These were propensity score matched 1:1 to unvaccinated patients. Time-to-amoxicillin was analysed using the Prior Event Rate Ratio (PERR) Pairwise method to address bias from time-invariant measured and unmeasured confounders. A simulation study and negative control outcome were used to help strengthen the validity of results.

Results

Compared to unvaccinated patients, those from the vaccinated group were more likely to be prescribed amoxicillin in the year prior to vaccination: hazard ratio (HR) 1.90 (95% confidence interval 1.83, 1.98). Following vaccination, the vaccinated group were again more likely to be prescribed amoxicillin, HR 1.64 (1.58,1.71). After adjusting for prior differences between the two groups using PERR Pairwise, overall vaccine effectiveness was 0.86 (0.81, 0.92). Additional analyses suggested that provided data meet the PERR assumptions, these estimates were robust.

Conclusions

Once differences between groups were taken into account, influenza vaccine had a beneficial effect, lowering the frequency of amoxicillin prescribing in the vaccinated group. Ensuring successful implementation of national programmes of vaccinating older adults against influenza may help contribute to reducing antibiotic resistance.

High-dimensional propensity scores improved the control of indication bias in surgical comparative effectiveness studies

OBJECTIVES

The objective of the study is to evaluate the performance of high-dimensional propensity scores (hdPSs) for controlling indication bias as compared with propensity scores (PSs) in surgical comparative effectiveness studies.

STUDY DESIGN AND SETTING

Patients who underwent interventional transcatheter aortic valve implantation (TAVI) or surgical aortic valve replacement (SAVR) between 2013 and 2017 were included from the French nationwide hospitals. At each hospital level, matched pairs of patients who underwent TAVI and SAVR were formed using PSs, considering 20 patient baseline characteristics, and hdPSs, considering the same patient characteristics and 300 additional variables from procedure and diagnosis codes the year before surgery. We compared death, reoperation, and stroke up to 3 years between TAVI and SAVR using Cox or Fine and Gray models.

RESULTS

Before matching, 12 of 20 patient characteristics were imbalanced between the included patients who underwent TAVI and SAVR. No significant imbalance persisted after matching with both methods. Hazard ratio of 1-year death, reoperation, and stroke was 1.3 [1.1; 1.4], 1.6 [1.1; 2.4], and 1.4 [1.2; 1.7] for TAVI relative to SAVR with PSs (n = 9,498 pairs) and 1.1 [1.0; 1.3], 1.3 [0.8; 2.0], and 1.3 [1.0; 1.6] with hdPSs (n = 7,157).

CONCLUSION

HdPS estimations were more consistent with results seen in randomized controlled trials. The HdPS is a promising alternative for the PS to control indication bias in comparative studies of surgical procedures.

Acupuncture reduced the medical expenditure in migraine patients: Real-world data of a 10-year national cohort study

OBJECTIVES

According to the data of Organisation for Economic Cooperation and Development, almost all the countries got increased medical expenditures in these years. Among the diseases, migraine is a condition that affects predominantly young and middle-aged people. It results in great economic losses. So we perform this research to investigate the acupuncture effect of reducing medical expenditure and medical resources use.

PERSPECTIVE

Acupuncture is a non-pharmacologic treatment and it became popular in recent years. In Taiwan, about 13% migraine patients visited acupuncture doctor. We hypothesized that the acupuncture had the additional effect than the medical treatment.

SETTING

We analysed the economic cost and medical visits in the real word.

METHODS

We used national cohort data from Taiwan, retrospectively gathered between 2000 and 2010. We selected newly diagnosed migraine patients who were diagnosed by registered neurologists formally licensed by the Taiwan Neurological Society. We divided these patients into two groups: with and without acupuncture treatment. The main outcome was medical expenditures and visits within 1 year after acupuncture.

RESULTS

In migraine patients who received acupuncture treatment, medical expenditures on emergency care and hospitalization were significantly lower than the group without acupuncture treatment.

CONCLUSION

According to our real-world data, acupuncture can reduce the medical expenditure in migraine patients within 1 year after diagnosis. For the health policy maker, it is cost effective to encourage combining acupuncture and western medicine to treat migraine patients. For the doctors in routine clinical practice, who may consider to consult acupuncture doctors to deal with the migraine patients together.

Intra-articular corticosteroid injections increase the risk of requiring knee arthroplasty

Aims

Recent studies have suggested that corticosteroid injections into the knee may harm the joint resulting in cartilage loss and possibly accelerating the progression of osteoarthritis (OA). The aim of this study was to assess whether patients with, or at risk of developing, symptomatic osteoarthritis of the knee who receive intra-articular corticosteroid injections have an increased risk of requiring arthroplasty.

Methods

We used data from the Osteoarthritis Initiative (OAI), a multicentre observational cohort study that followed 4,796 patients with, or at risk of developing, osteoarthritis of the knee on an annual basis with follow-up available up to nine years. Increased risk for symptomatic OA was defined as frequent knee symptoms (pain, aching, or stiffness) without radiological evidence of OA and two or more risk factors, while OA was defined by the presence of both femoral osteophytes and frequent symptoms in one or both knees. Missing data were imputed with multiple imputations using chained equations. Time-dependent propensity score matching was performed to match patients at the time of receving their first injection with controls. The effect of corticosteroid injections on the rate of subsequent (total and partial) knee arthroplasty was estimated using Cox proportional-hazards survival analyses.

Results

After removing patients lost to follow-up, 3,822 patients remained in the study. A total of 249 (31.3%) of the 796 patients who received corticosteroid injections, and 152 (5.0%) of the 3,026 who did not, had knee arthroplasty. In the matched cohort, Cox proportional-hazards regression resulted in a hazard ratio of 1.57 (95% confidence interval (CI) 1.37 to 1.81; p < 0.001) and each injection increased the absolute risk of arthroplasty by 9.4% at nine years’ follow-up compared with those who did not receive injections.

Conclusion

Corticosteroid injections seem to be associated with an increased risk of knee arthroplasty in patients with, or at risk of developing, symptomatic OA of the knee. These findings suggest that a conservative approach regarding the treatment of these patients with corticosteroid injections should be recommended. Cite this article: Bone Joint J 2020;102-B(5):586–592.

An interprofessional team training intervention with an implementation phase in a surgical ward: A controlled quasi-experimental study

Despite a growing awareness of the importance of interprofessional teamwork in relation to patient safety, many hospital units lack effective teamwork. The aim of this study was to explore if an interprofessional teamwork intervention in a surgical ward changed the healthcare personnel's perceptions of patient safety culture, perceptions of teamwork, and attitudes toward teamwork over 12 months. Healthcare personnel from surgical wards at two hospitals participated in a controlled quasi-experimental study. The intervention consisted of six hours of TeamSTEPPS team training and 12 months for the implementation of teamwork tools and strategies. The data collection was conducted among the healthcare personnel in the intervention group and the control group at baseline and at the end of the 12 month study period. The results within the intervention group showed that there were significantly improved scores in three of 12 patient safety culture dimensions and in three of five perceptions of teamwork dimensions after 12 months. When comparing between groups, significant differences were found in three patient safety culture measures in favor of the intervention group. The results of the study suggest that the teamwork intervention had a positive impact on patient safety culture and teamwork in the surgical ward.

Study methodology in trauma care: towards question-based study designs

The randomized controlled trial (RCT) in surgery may not always be ethical, feasible, or necessary to address a particular research question about the effect of a surgical intervention. If so, properly designed and conducted observational (non-randomized) studies may be valuable alternatives for an RCT and produce credible results. In this paper, we discus differences between RCTs and observational studies and differentiate between three types of comparisons of surgical interventions. We assert that results of different designs should be regarded as complementary to each other when evaluating surgical interventions. Criteria for credible observational research are presented to provide guidance for future observational research of surgical interventions. We argue that the research question that is being asked should guide the discussion about the value of a particular study design.

Estimating an Individual's Probability of Revision Surgery After Knee Replacement: A Comparison of Modeling Approaches Using a National Data Set

Tools that provide personalized risk prediction of outcomes after surgical procedures help patients make preference-based decisions among the available treatment options. However, it is unclear which modeling approach provides the most accurate risk estimation. We constructed and compared several parametric and nonparametric models for predicting prosthesis survivorship after knee replacement surgery for osteoarthritis. We used 430,455 patient-procedure episodes between April 2003 and September 2015 from the National Joint Registry for England, Wales, Northern Ireland, and the Isle of Man. The flexible parametric survival and random survival forest models most accurately captured the observed probability of remaining event-free. The concordance index for the flexible parametric model was the highest (0.705, 95% confidence interval (CI): 0.702, 0.707) for total knee replacement and was 0.639 (95% CI: 0.634, 0.643) for unicondylar knee replacement and 0.589 (95% CI: 0.586, 0.592) for patellofemoral replacement. The observed-to-predicted ratios for both the flexible parametric and the random survival forest approaches indicated that models tended to underestimate the risks for most risk groups. Our results show that the flexible parametric model has a better overall performance compared with other tested parametric methods and has better discrimination compared with the random survival forest approach.

Mendelian randomization: a novel approach for the prediction of adverse drug events and drug repurposing opportunities

Identification of unintended drug effects, specifically drug repurposing opportunities and adverse drug events, maximizes the benefit of a drug and protects the health of patients. However, current observational research methods are subject to several biases. These include confounding by indication, reverse causality and missing data. We propose that Mendelian randomization (MR) offers a novel approach for the prediction of unintended drug effects. In particular, we advocate the synthesis of evidence from this method and other approaches, in the spirit of triangulation, to improve causal inferences concerning drug effects. MR addresses some of the limitations associated with the existing methods in this field. Furthermore, it can be applied either before or after approval of the drug, and could therefore prevent the potentially harmful exposure of patients in clinical trials and beyond. The potential of MR as a pharmacovigilance and drug repurposing tool is yet to be realized, and could both help prevent adverse drug events and identify novel indications for existing drugs in the future.

Choice of time period to identify confounders for propensity score matching, affected the estimate: a retrospective cohort study of drug effectiveness in asthmatic children

OBJECTIVES

To control for confounding by indication in comparative (drug) effectiveness studies, propensity score (PS) methods may be used. Since childhood diseases or outcomes often present as acute events, we compared the effect of using different look-back periods in electronic health-care data, to construct PSs. This was applied in our research on the effect of a combination of inhaled corticosteroids/long-acting beta-2 agonists (ICS + LABA), either as fixed combination or used as loose combination (2 separate inhaler devices) in the prevention of severe asthma exacerbations.

METHODS

We created a cohort of children (5-17 years) diagnosed with asthma from the Dutch Integrated Primary Care information database. Within this cohort, we identified new users of ICS + LABA, either as fixed combination or loose combination (2 separate inhaler devices). The outcome of interest was severe asthma exacerbations. PSs for type of treatment were created using comorbidity and drug use history in different time windows: 1 week, 1 month, 3 months, 1 year, and full history prior to the start of treatment. PSs were used for matching subjects in both exposure groups. Time to first asthma exacerbation was analyzed with Cox proportional hazard regression. The results were compared with published clinical trials.

RESULTS

Of 39,682 asthmatic children, 3,500 (8.8%) were new users of either ICS + LABA fixed (3,324 [95.0%]) or loose (176 [5.0%]). The crude hazard ratio (HR) for a severe asthma exacerbation, comparing ICS + LABA fixed to loose was 0.37 (95% confidence interval [CI]: 0.20-0.66). PS-matched HRs (1 week, 1 month, 3 month, 1 year, and full history) were 0.48 (95% CI: 0.22-1.04); 0.60 (95% CI: 0.26-1.38), 0.69 (95% CI: 0.31-1.57), 0.56 (CI: 0.25-1.24), and 0.58 (CI: 0.24-1.36), respectively.

CONCLUSIONS

PS matching can be used to control for confounding in pediatric comparative (drug) effectiveness studies, the impact of different look-back periods to implement the PS is important. Controlling for confounders occurring in the 3 months preceding drug exposure may yield results comparable to clinical trial results.

A tutorial on the use of instrumental variables in pharmacoepidemiology

PURPOSE

Instrumental variable (IV) methods are used increasingly in pharmacoepidemiology to address unmeasured confounding. In this tutorial, we review the steps used in IV analyses and the underlying assumptions. We also present methods to assess the validity of those assumptions and describe sensitivity analysis to examine the effects of possible violations of those assumptions.

METHODS

Observational studies based on regression or propensity score analyses rely on the untestable assumption that there are no unmeasured confounders. IV analysis is a tool that removes the bias caused by unmeasured confounding provided that key assumptions (some of which are also untestable) are met.

RESULTS

When instruments are valid, IV methods provided unbiased treatment effect estimation in the presence of unmeasured confounders. However, the standard error of the IV estimate is higher than the standard error of non-IV estimates, e.g., regression and propensity score methods. Sensitivity analyses provided insight about the robustness of the IV results to the plausible degrees of violation of assumptions.

CONCLUSIONS

IV analysis should be used cautiously because the validity of IV estimates relies on assumptions that are, in general, untestable and difficult to be certain about. Thus, assessing the sensitivity of the estimate to violations of these assumptions is important and can better inform the causal inferences that can be drawn from the study. Copyright © 2017 John Wiley & Sons, Ltd.

How does work disability of patients with MS develop before and after diagnosis? A nationwide cohort study with a reference group

OBJECTIVES

We compared work disability of patients with multiple sclerosis (MS) from 5 years before with 5 years after diagnosis, with that of matched controls, and analysed whether progression in work disability among patients with MS was associated with sociodemography.

DESIGN

Population-based cohort study.

SETTING

The adult Swedish general population.

PARTICIPANTS

Residents aged 24-57 diagnosed with MS (n=3685) in 2003-2006 and 18 425 matched controls without MS.

PRIMARY AND SECONDARY OUTCOME MEASURES

Annual net days of sickness absence (SA) and disability pension (DP), used as a proxy for work disability, followed from 5 years before to 5 years after diagnosis (ie, T-5-T+5). For patients with MS, regression was used to identify sociodemographic factors related to progression in work disability.

RESULTS

Work disability of patients with MS increased gradually between T-5 and T-1 (mean: 46-82 days) followed by a sharp increase (T+1, 142 days), after which only a marginal increase was observed (T+5, 149 days). The matched controls had less work disability, slightly increasing during the period to a maximum of ∼40 days. Men with MS had a sharper increase in work disability before diagnosis. High educational level was associated with less progression in work disability before and around diagnosis.

CONCLUSIONS

Patients with MS had more work disability days also 5 years before diagnosis. Several sociodemographic variables were associated with the absolute level and the progression in SA and DP.

Human immunophenotyping via low-variance, low-bias, interpretive regression modeling of small, wide data sets: Application to aging and immune response to influenza vaccination

Small, wide data sets are commonplace in human immunophenotyping research. As defined here, a small, wide data set is constructed by sampling a small to modest quantity n,1 Collapse

Key Words

• Confidence interval
• Denoising
• Influenza
• Statistical assumptions
• Statistical bias
• Statistical regression modeling

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MESH Headings

• Adult
• Aging/immunology
• Analysis of Variance
• Antibodies, Viral/blood
• B-Lymphocytes/immunology
• Bias
• Cytokines/metabolism
• Datasets as Topic
• Humans
• Immunoglobulin A/blood
• Immunoglobulin G/blood
• Influenza Vaccines/immunology
• Influenza, Human/diagnosis
• Influenza, Human/epidemiology
• Influenza, Human/immunology
• Models, Theoretical
• Monitoring, Immunologic/methods
• Prognosis
• Regression Analysis

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Grants

• U19 AI057229 NIAID NIH HHS
• UL1 TR001085 NCATS NIH HHS

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Affiliation(s)

Tyson H Holmes Stanford University Human Immune Monitoring Center, Institute for Immunity, Transplantation and Infection, Stanford University School of Medicine, Stanford, CA 94305, USA.
Xiao-Song He Stanford University School of Medicine, 291 Campus Drive, Stanford, CA 94305, USA; VA Palo Alto Healthcare System, 3801 Miranda Avenue, Palo Alto, CA 94304, USA.

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Predicting Individual Survival After Hepatectomy for Hepatocellular Carcinoma: a Novel Nomogram from the "HCC East & West Study Group"

INTRODUCTIONS

Different staging systems have been devised for patients undergoing resection for hepatocellular carcinoma (HCC) with disparate results. The aim of this study was to create a new nomogram to predict individual survival after hepatectomy for HCC.

METHODS

Based on the "Hepatocellular Carcinoma: Eastern & Western Experiences Network," data from 2046 patients who underwent HCC resections at ten centers were reviewed. Patient survival was analyzed with Cox-regression analysis to construct a unique nomogram and contour plots to predict survival.

RESULTS

The nomograms built on the multivariate analyses, which showed that the independent predictors were tumor size, tumor number, vascular invasion, cirrhosis, preoperative bilirubin value, and esophageal varices, showed good calibration and discriminatory abilities with C-index value of 0.62 (95 % CI, 0.59-0.69) and 0.61 (95 % CI, 0.56-0.64) for overall and disease-free survival, respectively. The 5-year survival contour plots showed that the presence of vascular invasion was associated with decreased survival, regardless of the tumor number or size. Cirrhosis and varices were equally associated with decreased survival, according to the tumor number or size.

CONCLUSIONS

These nomograms accurately predict individual prognosis after HCC resection and support an expansion of the selection criteria for resection. They offer useful guidance to clinicians for individual survival prediction.

Variation between Hospitals with Regard to Diagnostic Practice, Coding Accuracy, and Case-Mix. A Retrospective Validation Study of Administrative Data versus Medical Records for Estimating 30-Day Mortality after Hip Fracture

BACKGROUND

The purpose of this study was to assess the validity of patient administrative data (PAS) for calculating 30-day mortality after hip fracture as a quality indicator, by a retrospective study of medical records.

METHODS

We used PAS data from all Norwegian hospitals (2005-2009), merged with vital status from the National Registry, to calculate 30-day case-mix adjusted mortality for each hospital (n = 51). We used stratified sampling to establish a representative sample of both hospitals and cases. The hospitals were stratified according to high, low and medium mortality of which 4, 3, and 5 hospitals were sampled, respectively. Within hospitals, cases were sampled stratified according to year of admission, age, length of stay, and vital 30-day status (alive/dead). The final study sample included 1043 cases from 11 hospitals. Clinical information was abstracted from the medical records. Diagnostic and clinical information from the medical records and PAS were used to define definite and probable hip fracture. We used logistic regression analysis in order to estimate systematic between-hospital variation in unmeasured confounding. Finally, to study the consequences of unmeasured confounding for identifying mortality outlier hospitals, a sensitivity analysis was performed.

RESULTS

The estimated overall positive predictive value was 95.9% for definite and 99.7% for definite or probable hip fracture, with no statistically significant differences between hospitals. The standard deviation of the additional, systematic hospital bias in mortality estimates was 0.044 on the logistic scale. The effect of unmeasured confounding on outlier detection was small to moderate, noticeable only for large hospital volumes.

CONCLUSIONS

This study showed that PAS data are adequate for identifying cases of hip fracture, and the effect of unmeasured case mix variation was small. In conclusion, PAS data are adequate for calculating 30-day mortality after hip-fracture as a quality indicator in Norway.

Methods to control for unmeasured confounding in pharmacoepidemiology: an overview

Background Unmeasured confounding is one of the principal problems in pharmacoepidemiologic studies. Several methods have been proposed to detect or control for unmeasured confounding either at the study design phase or the data analysis phase. Aim of the Review To provide an overview of commonly used methods to detect or control for unmeasured confounding and to provide recommendations for proper application in pharmacoepidemiology. Methods/Results Methods to control for unmeasured confounding in the design phase of a study are case only designs (e.g., case-crossover, case-time control, self-controlled case series) and the prior event rate ratio adjustment method. Methods that can be applied in the data analysis phase include, negative control method, perturbation variable method, instrumental variable methods, sensitivity analysis, and ecological analysis. A separate group of methods are those in which additional information on confounders is collected from a substudy. The latter group includes external adjustment, propensity score calibration, two-stage sampling, and multiple imputation. Conclusion As the performance and application of the methods to handle unmeasured confounding may differ across studies and across databases, we stress the importance of using both statistical evidence and substantial clinical knowledge for interpretation of the study results.

Head to head comparison of the propensity score and the high-dimensional propensity score matching methods

BACKGROUND

Comparative performance of the traditional propensity score (PS) and high-dimensional propensity score (hdPS) methods in the adjustment for confounding by indication remains unclear. We aimed to identify which method provided the best adjustment for confounding by indication within the context of the risk of diabetes among patients exposed to moderate versus high potency statins.

METHOD

A cohort of diabetes-free incident statins users was identified from the Quebec's publicly funded medico-administrative database (Full Cohort). We created two matched sub-cohorts by matching one patient initiated on a lower potency to one patient initiated on a high potency either on patients' PS or hdPS. Both methods' performance were compared by means of the absolute standardized differences (ASDD) regarding relevant characteristics and by means of the obtained measures of association.

RESULTS

Eight out of the 18 examined characteristics were shown to be unbalanced within the Full Cohort. Although matching on either method achieved balance within all examined characteristic, matching on patients' hdPS created the most balanced sub-cohort. Measures of associations and confidence intervals obtained within the two matched sub-cohorts overlapped.

CONCLUSION

Although ASDD suggest better matching with hdPS than with PS, measures of association were almost identical when adjusted for either method. Use of the hdPS method in adjusting for confounding by indication within future studies should be recommended due to its ability to identify confounding variables which may be unknown to the investigators.

Effect of telehealth on hospital utilisation and mortality in routine clinical practice: a matched control cohort study in an early adopter site

OBJECTIVES

To assess the effects of a home-based telehealth intervention on the use of secondary healthcare and mortality.

DESIGN

Observational study of a mainstream telehealth service, using person-level administrative data. Time to event analysis (Cox regression) was performed comparing telehealth patients with controls who were matched using a machine-learning algorithm.

SETTING

A predominantly rural region of England (North Yorkshire).

PARTICIPANTS

716 telehealth patients were recruited from community, general practice and specialist acute care, between June 2010 and March 2013. Patients had chronic obstructive pulmonary disease, congestive heart failure or diabetes, and a history of associated inpatient admission. Patients were matched 1:1 to control patients, also selected from North Yorkshire, with respect to demographics, diagnoses of health conditions, previous hospital use and predictive risk score.

INTERVENTIONS

Telehealth involved the remote exchange of medical data between patients and healthcare professionals as part of the ongoing management of the patient's health condition. Monitoring centre staff alerted healthcare professionals if the telemonitored data exceeded preset thresholds. Control patients received usual care, without telehealth.

PRIMARY AND SECONDARY OUTCOME MEASURES

Time to the first emergency (unplanned) hospital admission or death. Secondary metrics included time to death and time to first admission, outpatient attendance and emergency department visit.

RESULTS

Matched controls and telehealth patients were similar at baseline. Following enrolment, telehealth patients were more likely than matched controls to experience emergency admission or death (adjusted HR 1.34, 95% CI 1.16 to 1.56, p<0.001). They were also more likely to have outpatient attendances (adjusted HR=1.25, 1.11 to 1.40, p<0.001), but mortality rates were similar between groups. Sensitivity analyses showed that we were unlikely to have missed reductions in the likelihood of an emergency admission or death because of unobserved baseline differences between patient groups.

CONCLUSIONS

Telehealth was not associated with a reduction in secondary care utilisation.

Birth cohort appeared to confound effect estimates of guideline changes on statin utilization

OBJECTIVES

To investigate how birth cohorts can confound population-based intervention effect estimates.

STUDY DESIGN AND SETTING

Interrupted time series design was applied to study the prevalence of statin use in Dutch diabetes patients over the period 1998-2011. Effects of guideline changes on the outcome were estimated using a Poisson regression model with and without the birth cohort dimension modeled through random intercepts.

RESULTS

Both models estimated a stronger increase in prevalence of statin use after influential studies were published in 2003 for patients aged below 50 and above 70 years. The model that controlled for birth cohort also estimated an effect for patients aged 50-70 years from 2003 onward. The magnitude of the intervention effect for patients aged above 70 years when we controlled for birth cohort was reduced from 0.078 [95% confidence interval (CI): 0.065, 0.091] to 0.027 (95% CI: 0.013, 0.041). Similarly, for patients aged below 50 years, the estimated guideline effect was reduced from 0.070 (95% CI: 0.048, 0.092) to 0.055 (95% CI: 0.035, 0.075).

CONCLUSION

In this case study, the birth cohort dimension appeared to confound population-level effect estimates of guideline changes on prevalence of statin use in patients with diabetes.

Bayesian immunological model development from the literature: example investigation of recent thymic emigrants

Bayesian estimation techniques offer a systematic and quantitative approach for synthesizing data drawn from the literature to model immunological systems. As detailed here, the practitioner begins with a theoretical model and then sequentially draws information from source data sets and/or published findings to inform estimation of model parameters. Options are available to weigh these various sources of information differentially per objective measures of their corresponding scientific strengths. This approach is illustrated in depth through a carefully worked example for a model of decline in T-cell receptor excision circle content of peripheral T cells during development and aging. Estimates from this model indicate that 21 years of age is plausible for the developmental timing of mean age of onset of decline in T-cell receptor excision circle content of peripheral T cells.

After adjusting for bias in meta-analysis seasonal influenza vaccine remains effective in community-dwelling elderly

OBJECTIVE

To compare the performance of the bias-adjusted meta-analysis to the conventional meta-analysis assessing seasonal influenza vaccine effectiveness among community-dwelling elderly aged 60 years and older.

STUDY DESIGN AND SETTING

Systematic literature search revealed 14 cohort studies that met inclusion and exclusion criteria. Laboratory-confirmed influenza, influenza-like illness, hospitalization from influenza and/or pneumonia, and all-cause mortality were study outcomes. Potential biases were identified using bias checklists. The magnitude and uncertainty of biases were assessed by expert opinion. Pooled odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated using random effects model.

RESULTS

After incorporating biases, overall effect estimates regressed slightly toward no effect, with the largest relative difference between conventional and bias-adjusted ORs for laboratory-confirmed influenza (OR, 0.18; 95% CI: 0.01, 3.00 vs. OR, 0.23; 95% CI: 0.03, 2.04). In most of the studies, CIs widened reflecting uncertainties about the biases. The between-study heterogeneity reduced considerably with the largest reduction for all-cause mortality (I(2) = 4%, P = 0.39 vs. I(2) = 91%, P < 0.01).

CONCLUSION

This case study showed that after addressing potential biases influenza vaccine was still estimated effective in preventing hospitalization from influenza and/or pneumonia and all-cause mortality. Increasing the number of assessors and incorporating empirical evidence might improve the new bias-adjustment method.

The effects of the timing of spinal surgery after traumatic spinal cord injury: a systematic review and meta-analysis

Abstract The debate over the effects of the timing of surgical spinal decompression after traumatic spinal cord injury (tSCI) has remained unresolved for over a century. The aim of the current study was to perform a systematic review and quality-adjusted meta-analysis of studies evaluating the effects of the timing of spinal surgery after tSCI. Studies were searched for through the MEDLINE(®) database (1966 to August 2012) and a 15-item, tailored scoring system was used for assessing the included studies' susceptibility to bias. Random effects and quality effects meta-analyses were performed. Models were tested for robustness using one way and criterion-based sensitivity analysis and funnel plots. Results are presented as weighted mean differences (WMDs) and odds ratios (ORs) with 95% confidence intervals (CIs). A total of 18 studies were analyzed. Heterogeneity was evident among the studies included. Quality effects models showed that - when compared with "late" surgery - "early" spinal surgery was significantly associated with a higher total motor score improvement (WMD: 5.94 points, 95% CI:0.74,11.15) in seven studies, neurological improvement rate (OR: 2.23, 95% CI:1.35,3.67) in six studies, and shorter length of hospital stay (WMD: -9.98 days, 95% CI:-13.10,-6.85) in six studies. However, one way and criterion-based sensitivity analyses demonstrated a profound lack of robustness among pooled estimates. Funnel plots showed significant proof of publication bias. In conclusion, despite the fact that "early" spinal surgery was significantly associated with improved neurological and length of stay outcomes, the evidence supporting "early" spinal surgery after tSCI lacks robustness as a result of different sources of heterogeneity within and between original studies. Where the conduct of a surgical, randomized controlled trial seems to be an unfeasible undertaking in acute tSCI, methodological safeguards require the utmost attention in future cohort studies. (Prospero registration number: PROSPERO CRD42012003182. See also http://www.crd.york.ac.uk/NIHR_PROSPERO/ ).

Effect of telephone health coaching (Birmingham OwnHealth) on hospital use and associated costs: cohort study with matched controls

OBJECTIVES

To test the effect of a telephone health coaching service (Birmingham OwnHealth) on hospital use and associated costs.

DESIGN

Analysis of person level administrative data. Difference-in-difference analysis was done relative to matched controls.

SETTING

Community based intervention operating in a large English city with industry.

PARTICIPANTS

2698 patients recruited from local general practices before 2009 with heart failure, coronary heart disease, diabetes, or chronic obstructive pulmonary disease; and a history of inpatient or outpatient hospital use. These individuals were matched on a 1:1 basis to control patients from similar areas of England with respect to demographics, diagnoses of health conditions, previous hospital use, and a predictive risk score.

INTERVENTION

Telephone health coaching involved a personalised care plan and a series of outbound calls usually scheduled monthly. Median length of time enrolled on the service was 25.5 months. Control participants received usual healthcare in their areas, which did not include telephone health coaching.

MAIN OUTCOME MEASURES

Number of emergency hospital admissions per head over 12 months after enrolment. Secondary metrics calculated over 12 months were: hospital bed days, elective hospital admissions, outpatient attendances, and secondary care costs.

RESULTS

In relation to diagnoses of health conditions and other baseline variables, matched controls and intervention patients were similar before the date of enrolment. After this point, emergency admissions increased more quickly among intervention participants than matched controls (difference 0.05 admissions per head, 95% confidence interval 0.00 to 0.09, P=0.046). Outpatient attendances also increased more quickly in the intervention group (difference 0.37 attendances per head, 0.16 to 0.58, P<0.001), as did secondary care costs (difference £175 per head, £22 to £328, P=0.025). Checks showed that we were unlikely to have missed reductions in emergency admissions because of unobserved differences between intervention and matched control groups.

CONCLUSIONS

The Birmingham OwnHealth telephone health coaching intervention did not lead to the expected reductions in hospital admissions or secondary care costs over 12 months, and could have led to increases.

The role of exercise in modifying outcomes for people with multiple sclerosis: a randomized trial

BACKGROUND

Despite the commonly known benefits of exercise and physical activity evidence shows that persons Multiple Sclerosis (MS) are relatively inactive yet physical activity may be even more important in a population facing functional deterioration. No exercise is effective if it is not done and people with MS face unique barriers to exercise engagement which need to be overcome. We have developed and pilot tested a Multiple Sclerosis Tailored Exercise Program (MSTEP) and it is ready to be tested against general guidelines for superiority and ultimately for its impact on MS relevant outcomes. The primary research question is to what extent does an MS Tailored Exercise Program (MSTEP) result in greater improvements in exercise capacity and related outcomes over a one year period in comparison to a program based on general guidelines for exercise among people with MS who are sedentary and wish to engage in exercise as part of MS self-management.

METHODS/DESIGN

The proposed study is an assessor-blind, parallel-group, randomized controlled trial (RCT). The duration of the intervention will be one year with follow-up to year two. The targeted outcomes are exercise capacity, functional ambulation, strength, and components of quality of life including frequency and intensity of fatigue symptoms, mood, global physical function, health perception, and objective measures of activity level. Logistic regression will be used to test the main hypothesis related to the superiority of the MSTEP program based on a greater proportion of people making a clinically relevant gain in exercise capacity at 1 year and at 2 years, using an intention-to-treat approach. Sample size will be 240 (120 per group).

DISCUSSION

The MS community is clearly looking for interventions to help alleviate the disabling sequelae of MS and promote health. Exercise is a well-known intervention which has known benefits to all, yet few exercise regularly. For people with MS, the role of exercise in MS management needs to be rigorously assessed to inform people as to how best to use exercise to reduce disability and promote health.

TRIAL REGISTRATION

Clinical Trials.gov: NCT01611987.

Impact of cardiovascular calcifications on the detrimental effect of continued smoking on cardiovascular risk in male lung cancer screening participants

Background

Current smokers have an increased cardiovascular disease (CVD) risk compared to ex-smokers due to reversible as well as irreversible effects of smoking. We investigated if current smokers remain to have an increased CVD risk compared to ex-smokers in subjects with a long and intense smoking history. We in addition studied if the effect of smoking continuation on CVD risk is independent of or modified by the presence of cardiovascular calcifications.

Methods

The cohort used comprised a sample of 3559 male lung cancer screening trial participants. We conducted a case-cohort study using all CVD cases and a random sample of 10% (n = 341) from the baseline cohort (subcohort). A weighted Cox proportional hazards model was used to estimate the hazard ratios for current smoking status in relation to CVD events.

Results

During a median follow-up of 2.6 years (max. 3.7 years), 263 fatal and non-fatal cardiovascular events (cases) were identified. Age, packyears and cardiovascular calcification adjusted hazard ratio of current smokers compared to former smokers was 1.33 (95% confidence interval 1.00–1.77). In additional analyses that incorporated multiplicative interaction terms, neither coronary nor aortic calcifications modified the association between smoking status and cardiovascular risk (P = 0.08).

Conclusions

Current smokers have an increased CVD risk compared to former smokers even in subjects with a long and intense smoking history. Smoking exerts its hazardous effects on CVD risk by pathways partly independent of cardiovascular calcifications.

β-Blockers and All-Cause Mortality in Adults with Episodes of Acute Bronchitis: An Observational Study

BACKGROUND

Recent observational studies suggest that β-blockers may improve long-term prognosis in patients with chronic obstructive pulmonary disease (COPD). We assessed whether β-blocker use improves all-cause mortality in patients with episodes of acute bronchitis.

METHODS

An observational cohort study using data from the electronic medical records of 23 general practices in the Netherlands. The data included standardized information about daily patient contacts, diagnoses, and drug prescriptions. Cox regression was applied with time-varying treatment and covariates.

RESULTS

The study included 4,493 patients aged 45 years and older, with at least one episode of acute bronchitis between 1996 and 2006. The mean (SD) age of the patients was 66.9 (11.7) years, and 41.9% were male. During a mean (SD) follow up period of 7.7 (2.5) years, 20.4% developed COPD. In total, 22.7% had cardiovascular comorbidities, resulting in significant higher mortality rates than those without (51.7% vs. 12.0%, p<0.001). The adjusted hazard ratio of cardioselective β-blocker use for mortality was 0.62 (95% confidence interval [CI], 0.50-0.77), and 1.01 (95% CI 0.75-1.36) for non-selective ones. Some other cardiovascular drugs also reduced the risk of mortality, with adjusted HRs of 0.60 (95% CI 0.46-0.79) for calcium channel blockers, 0.88 (95% CI 0.73-1.06) for ACE inhibitors/angiotensin receptor blockers, and 0.42 (95% CI 0.31-0.57) for statins, respectively.

CONCLUSION

Cardiovascular comorbidities are common and increase the risk of mortality in adults with episodes of acute bronchitis. Cardioselective β-blockers, but also calcium channel blockers and statins may reduce mortality, possibly as a result of cardiovascular protective properties.

A methodological systematic review on surgical site infections following spinal surgery: part 1: risk factors

STUDY DESIGN

A methodological systematic review.

OBJECTIVE

To critically appraise the validity of risk factors for surgical site infection (SSI) after spinal surgery.

SUMMARY OF BACKGROUND DATA

SSIs lead to higher morbidity, mortality, and increased health care costs. Understanding which factors lead to an increased risk of SSI is important for the development of prophylactic protocols to counter this risk. To date, however, no review appraising the methodological quality of studies evaluating risk factors for spinal SSIs has been published.

METHODS

Contemporary studies identifying risk factors for SSI after spinal surgery were searched through the Medline and EMBASE databases (January 2001 to December 2010). References were retrieved and bias-prone study features were abstracted individually and independently by 2 authors.

RESULTS

Twenty-four eligible studies were identified, including 9 (nested) case-control studies and 15 case series. Included studies covered wide variations of indications and surgical procedures. A total of 73 different types of factors were evaluated for the risk of an SSI of which 34 (47%) were reported to be significantly related to at least 1 study. Only the following risk factors-diabetes mellitus, obesity, and previous SSI-were confirmed more often (n = 11, 8, and 3, respectively) as a significant risk factor for an SSI than they were disproved (n = 7, 6, and 1, respectively). Various sources of heterogeneity were observed, including patient selection, selection and analysis of putative risk factors, and definitions of SSI outcomes.

CONCLUSION

There is an abundance of conflicting data on risk factors for SSI after spinal surgery. Given various sources of heterogeneity observed in observational literature, there is a paucity of solid evidence for the proof of robust risk factors. The authors recommend the introduction, validation, and use of a standardized set of strongly justified eligibility criteria and well-defined candidate risk factors and spinal SSI outcomes.

Combining directed acyclic graphs and the change-in-estimate procedure as a novel approach to adjustment-variable selection in epidemiology

Background

Directed acyclic graphs (DAGs) are an effective means of presenting expert-knowledge assumptions when selecting adjustment variables in epidemiology, whereas the change-in-estimate procedure is a common statistics-based approach. As DAGs imply specific empirical relationships which can be explored by the change-in-estimate procedure, it should be possible to combine the two approaches. This paper proposes such an approach which aims to produce well-adjusted estimates for a given research question, based on plausible DAGs consistent with the data at hand, combining prior knowledge and standard regression methods.

Methods

Based on the relationships laid out in a DAG, researchers can predict how a collapsible estimator (e.g. risk ratio or risk difference) for an effect of interest should change when adjusted on different variable sets. Implied and observed patterns can then be compared to detect inconsistencies and so guide adjustment-variable selection.

Results

The proposed approach involves i. drawing up a set of plausible background-knowledge DAGs; ii. starting with one of these DAGs as a working DAG, identifying a minimal variable set, S, sufficient to control for bias on the effect of interest; iii. estimating a collapsible estimator adjusted on S, then adjusted on S plus each variable not in S in turn (“add-one pattern”) and then adjusted on the variables in S minus each of these variables in turn (“minus-one pattern”); iv. checking the observed add-one and minus-one patterns against the pattern implied by the working DAG and the other prior DAGs; v. reviewing the DAGs, if needed; and vi. presenting the initial and all final DAGs with estimates.

Conclusion

This approach to adjustment-variable selection combines background-knowledge and statistics-based approaches using methods already common in epidemiology and communicates assumptions and uncertainties in a standardized graphical format. It is probably best suited to areas where there is considerable background knowledge about plausible variable relationships. Researchers may use this approach as an additional tool for selecting adjustment variables when analyzing epidemiological data.

Research design considerations for clinical studies of abuse-deterrent opioid analgesics: IMMPACT recommendations

Opioids are essential to the management of pain in many patients, but they also are associated with potential risks for abuse, overdose, and diversion. A number of efforts have been devoted to the development of abuse-deterrent formulations of opioids to reduce these risks. This article summarizes a consensus meeting that was organized to propose recommendations for the types of clinical studies that can be used to assess the abuse deterrence of different opioid formulations. Because of the many types of individuals who may be exposed to opioids, an opioid formulation will need to be studied in several populations using various study designs to determine its abuse-deterrent capabilities. It is recommended that the research conducted to evaluate abuse deterrence should include studies assessing: (1) abuse liability, (2) the likelihood that opioid abusers will find methods to circumvent the deterrent properties of the formulation, (3) measures of misuse and abuse in randomized clinical trials involving pain patients with both low risk and high risk of abuse, and (4) postmarketing epidemiological studies.

Balance measures for propensity score methods: a clinical example on beta-agonist use and the risk of myocardial infarction

PURPOSE

Propensity score (PS) methods aim to control for confounding by balancing confounders between exposed and unexposed subjects with the same PS. PS balance measures have been compared in simulated data but limited in empirical data. Our objective was to compare balance measures in clinical data and assessed the association between long-acting inhalation beta-agonist (LABA) use and myocardial infarction.

METHODS

We estimated the relationship between LABA use and myocardial infarction in a cohort of adults with a diagnosis of asthma or chronic obstructive pulmonary disorder from the Utrecht General Practitioner Research Network database. More than two thousand PS models, including information on the observed confounders age, sex, diabetes, cardiovascular disease and chronic obstructive pulmonary disorder status, were applied. The balance of these confounders was assessed using the standardised difference (SD), Kolmogorov-Smirnov (KS) distance and overlapping coefficient. Correlations between these balance measures were calculated. In addition, simulation studies were performed to assess the correlation between balance measures and bias.

RESULTS

LABA use was not related to myocardial infarction after conditioning on the PS (median heart rate = 1.14, 95%CI = 0.47-2.75). When using the different balance measures for selecting a PS model, similar associations were obtained. In our empirical data, SD and KS distance were highly correlated balance measures (r = 0.92). In simulations, SD, KS distance and overlapping coefficient were similarly correlated to bias (e.g. r = 0.55, r = 0.52 and r = -0.57, respectively, when conditioning on the PS).

CONCLUSIONS

We recommend using the SD or the KS distance to quantify the balance of confounder distributions when applying PS methods.

Comparative study of cisplatin and epirubicin in transcatheter arterial chemoembolization for hepatocellular carcinoma

AIM

  Transcatheter arterial chemoembolization (TACE) is an established treatment for unresectable hepatocellular carcinoma (HCC). However, it is unclear which chemotherapeutic agent should be selected for TACE. The aim of this study was to compare the efficacy of cisplatin (CDDP) with that of epirubicin (EPI) in TACE for patients with unresectable or relapsed HCC.

METHODS

  We performed a historical cohort study involving 131 patients treated with a first TACE, defined as either an initial treatment for previously untreated HCC or a first treatment for relapsed HCC after curative resections or ablations. Efficacy was estimated as the response rate (RR) and it was adjusted for the confounding factors that were defined in this study.

RESULTS

  The RR were 62.5% (20/32) for the first TACE with CDDP and 51.5% (51/99) for that with EPI. In the adjusted analysis for a history of hepatectomy, percutaneous treatment combined with TACE and tumor factors, the odds ratio was 1.72 (95% confidence interval [CI] = 0.70-4.48). However, a test for interaction between the number of tumors and the chemotherapeutic agent was statistically significant (P = 0.016). In multiple HCC, the RR were 66.7% (10/17) for CDDP and 39.6% (30/46) for EPI. The odds ratio was 4.11 (95% CI = 1.14-17.2).

CONCLUSION

  CDDP may be more effective than EPI in TACE for multiple HCC. A randomized controlled study is needed to clarify the efficacy of CDDP in TACE in patients with multiple HCC.

Sensitivity analysis for an unmeasured confounder: a review of two independent methods

One of the main purposes of epidemiological studies is to estimate causal effects. Causal inference should be addressed by observational and experimental studies. A strong constraint for the interpretation of observational studies is the possible presence of unobserved confounders (hidden biases). An approach for assessing the possible effects of unobserved confounders may be drawn up through the use of a sensitivity analysis that determines how strong the effects of an unmeasured confounder should be to explain an apparent association, and which should be the characteristics of this confounder to exhibit such an effect. The purpose of this paper is to review and integrate two independent sensitivity analysis methods. The two methods are presented to assess the impact of an unmeasured confounder variable: one developed by Greenland under an epidemiological perspective, and the other developed from a statistical standpoint by Rosenbaum. By combining (or merging) epidemiological and statistical issues, this integration became a more complete and direct sensitivity analysis, encouraging its required diffusion and additional applications. As observational studies are more subject to biases and confounding than experimental settings, the consideration of epidemiological and statistical aspects in sensitivity analysis strengthens the causal inference.

Instrumental variables in influenza vaccination studies: mission impossible?!

OBJECTIVES

Unobserved confounding has been suggested to explain the effect of influenza vaccination on mortality reported in several observational studies. An instrumental variable (IV) is strongly related to the exposure under study, but not directly or indirectly (through other variables) with the outcome. Theoretically, analyses using IVs to control for both observed and unobserved confounding may provide unbiased estimates of influenza vaccine effects. We assessed the usefulness of IV analysis in influenza vaccination studies.

METHODS

Information on patients aged 65 years and older from the computerized Utrecht General Practitioner (GP) research database over seven influenza epidemic periods was pooled to estimate the association between influenza vaccination and all-cause mortality among community-dwelling elderly. Potential IVs included in the analysis were a history of gout, a history of orthopaedic morbidity, a history of antacid medication use, and GP-specific vaccination rates.

RESULTS

Using linear regression analyses, all possible IVs were associated with vaccination status: risk difference (RD) 7.8% (95% confidence interval [CI] 3.6%; 12.0%), RD 2.8% (95% CI 1.7%; 3.9%), RD 8.1% (95% CI 6.1%; 10.1%), and RD 100.0% (95% CI 89.0%; 111.0%) for gout, orthopaedic morbidity, antacid medication use, and GP-specific vaccination rates, respectively. Each potential IV, however, also appeared to be related to mortality through other observed confounding variables (notably age, sex, and comorbidity).

CONCLUSIONS

The potential IVs studied did not meet the necessary criteria, because they were (indirectly) associated with the outcome. These variables may, therefore, not be suited to assess unconfounded influenza vaccine effects through IV analysis.

The impact of concurrent heart failure on prognosis in patients with chronic obstructive pulmonary disease

AIMS

To compare prognosis in patients with chronic obstructive pulmonary disease (COPD) with or without concomitant heart failure.

METHODS AND RESULTS

Patients aged 65 years or over with a general practitioner (GP)'s diagnosis of COPD but without a prior diagnosis of heart failure underwent an extensive diagnostic work-up including echocardiography and pulmonary function tests in the period 2001-03. An expert panel then confirmed the presence or absence of COPD according to the GOLD criteria and (previously undiagnosed) heart failure according to the criteria of the ESC heart failure guidelines. This cohort of 405 patients was followed up for a mean duration of 4.2 (SD 1.4) years. The GP's electronic medical files relating to the participants, including any specialist letters, were scrutinized until April 2007 for information about drug use, exacerbations of COPD, pneumonia, hospitalizations, death, and cause of death. The mean age of patients at the start of the study was 73.0 (SD 5.3) years, and 54% were male. The presence of newly detected heart failure significantly increased all-cause mortality independent of gender, age, history of ischaemic heart disease, hypertension, diabetes mellitus, atrial fibrillation, smoking, and cardiovascular drug use at baseline (adjusted hazard ratio, 2.1; 95% confidence interval, 1.2-3.6; P = 0.01).

CONCLUSION

Heart failure is a strong independent predictor of all-cause mortality in patients with a diagnosis of COPD.